Pathophysiology
Summary
Inflammatory bowel disease (IBD) predominantly affects young individuals and present with symptoms such as fever, weight loss, abdominal pain, and diarrhea. IBD most commonly manifests as ulcerative colitis or Crohn’s disease, both of which can lead to various extraintestinal manifestations such as arthritis, erythema nodosum, pyoderma gangrenosum, renal calculi, and eye diseases like uveitis & iritis. Treatment for IBD involves 5-ASA agents like sulfasalazine and mesalamine
Ulcerative colitis (UC) always involves the rectum and spreads proximally in a continuous pattern, and is often associated with p-ANCA antibodies. UC presents as a ‘lead pipe’ appearance on contrast enema, and is restricted to the mucosa and submucosa. Histology often reveals abscesses within the colonic crypts and the presence of ‘pseudopolyps’—islands of normal mucosa within ulcerated tissue. Clinically, it presents with left-sided abdominal pain and bloody diarrhea. Notable complications include toxic megacolon, which can progress to colonic perforation, and an increased risk for colon cancer. UC is also strongly associated with primary sclerosing cholangitis.
Crohn's disease is characterized by skip lesions, affecting any portion of the GI tract in a discontinuous manner. It is often associated with anti-Saccharomyces cerevisiae antibodies and often manifest clinically as RLQ pain and malabsorption, particularly of fats and fat-soluble vitamins. Unlike UC, Crohn's disease causes transmural inflammation, which can result in noncaseating granulomas, fistulas, and fibrotic strictures. These strictures can lead to bowel obstruction, often visible as the ‘string sign’ on X-ray.
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FAQs
Ulcerative colitis specifically targets the rectum and extends proximally in a continuous pattern, affecting only the mucosal and submucosal layers of the colon. It is characterized by a "lead pipe" appearance on contrast enema due to the loss of normal haustral projections. In contrast, Crohn's disease can affect any part of the gastrointestinal tract and leads to transmural inflammation, resulting in "skip lesions," which are diseased areas interspersed with normal bowel segments.
Inflammatory bowel disease (IBD) manifests with a range of symptoms including fever, weight loss, abdominal pain, and diarrhea. The location of abdominal pain can hint at the specific type of IBD: left-sided abdominal pain is common in ulcerative colitis, while right lower quadrant (RLQ) pain is often reported in Crohn's disease. Diarrhea is a symptom in both conditions; however, it is frequently bloody in ulcerative colitis due to rectal inflammation, whereas in Crohn's disease, it is often related to malabsorption of fats and fat-soluble vitamins.
Ulcerative colitis may result in toxic megacolon, a condition where inflammation extends to the colonic smooth muscle, causing severe colonic dilation and potentially leading to perforation. It also increases the risk of colon cancer. Crohn's disease can cause fibrotic strictures due to transmural inflammation, leading to a thickened bowel wall and narrowed lumen, which may result in bowel obstruction. Additionally, Crohn's can lead to the formation of fistulas between the bowel and other organs.
In ulcerative colitis, perinuclear anti-neutrophil cytoplasmic antibodies (pANCA) are often elevated. Histological examination may reveal abscesses within colonic crypts and the presence of ‘pseudopolyps,' which are islands of normal mucosa within ulcerated tissue. In Crohn's disease, anti-saccharomyces cerevisiae antibodies are commonly present. X-ray imaging may show a "string sign" due to fibrotic strictures, and histology often reveals noncaseating granulomas containing aggregations of macrophages.
Inflammatory bowel disease (IBD) can lead to a variety of systemic complications. Arthritis forms like migratory polyarthritis, sacroiliitis, and ankylosing spondylitis are common and often associated with the HLA-B27 gene. Skin conditions such as erythema nodosum, characterized by painful erythematous nodular rashes on the shins, and pyoderma gangrenosum, which involves skin ulcers, can also occur. Eye diseases like anterior uveitis, iritis, and episcleritis can result in eye pain and redness. Additionally, IBD can cause renal calculi due to the increased absorption of oxalate.
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